Implement support for `--exclude <req>`. #2293

Job	Run time
Check GitHub Organization	1s
tox -e format-check,typecheck,vendor-check,package	4m 16s
tox -e py312-pip23_3_1	18m 48s
./dtox.sh -e py27-pip20	11m 39s
tox -e py312-pip23_3_1-integration	46m 6s
./dtox.sh -e py35-pip20	20m 13s
./dtox.sh -e py311-pip20	19m 19s
./dtox.sh -e py311-pip22_3_1	24m 2s
./dtox.sh -e py311-pip23_1_2	15m 11s
./dtox.sh -e py312-pip23_3_1	14m 16s
./dtox.sh -e pypy310-pip20	27m 40s
./dtox.sh -e pypy310-pip22_3_1	27m 48s
./dtox.sh -e pypy310-pip23_1_2	28m 7s
./dtox.sh -e py27-pip20-integration	29m 34s
./dtox.sh -e py37-pip22_3_1-integration	1h 35m 15s
./dtox.sh -e py37-pip23_1_2-integration	1h 19m 43s
./dtox.sh -e py311-pip20-integration	20m 54s
./dtox.sh -e py311-pip22_3_1-integration	27m 30s
./dtox.sh -e py311-pip23_1_2-integration	27m 15s
./dtox.sh -e py312-pip23_3_1-integration	35m 8s
./dtox.sh -e pypy310-pip20-integration	1h 16m 54s
./dtox.sh -e pypy310-pip22_3_1-integration	52m 44s
./dtox.sh -e pypy310-pip23_1_2-integration	50m 20s
Gather Final Status	1s
	12h 32m 44s

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